Hi there. Great work you've done here, and quite ambitious. Congrats and have some rep!

Concerning your "blank spot". It all comes down to latitude, really:
- If close to the equator, then you will definitely have to include some rivers as that area seems to be large enough to sustain its own convective centers, meaning it will rain and a lot and you will have tropical forest (think Amazon basin or Congo Basin).
- Further north (or south) but before the tropics (roughly 23º N/S) it will be savannah, without significant rivers (since it's away from the coasts and shielded by mountains on both east and west).
- Close to the tropics and poleward, that will surely be a desert, a hot and dry desert, be it sandy or rocky.
- Above that, forest - sparse, trees are deciduous and adapted to dry spells, then grassland, then forest - mixed, then forest conifers only, then tundra, then permament ice.

Looking at where it lies in the overall map, and assuming north is up, I'd go for the equatorial or tropical choices, depending on where you want your deserts.

Bottom line is... what's the latitude scale?